Yunus Rahmatullah was captured by British special forces in Iraq in 2004 and handed over to US troops soon afterwards. The incident was initially kept secret from ministers and only disclosed to MPs five years later, in 2009. Rahmatullah, now 31, was released by the US without charge in May.

He is believed to have been first held at Camp Nama, a secret detention facility at Baghdad airport that British troops helped to run. He was later transferred to Iraq’s notorious Abu Ghraib jail before being rendered to the Bagram “black prison” in Afghanistan.

The court of appeal ruled in 2011 that Rahmatullah was unlawfully detained and ordered a writ of habeas corpus – the ancient British legal right to be charged or released from arbitrary detention – to be issued.

However, lawyers acting for the government later successfully argued in the supreme court that British ministers had no power “to direct the US” to release Rahmatullah from Bagram.

He describes in detail his torture and abuse in a 60-page document drawn up by his lawyers and seen by the Guardian. He says when he was captured by British special forces in Iraq in early 2004 he was beaten unconscious. Soldiers cut his clothes with a pair of scissors until, he says, he was “completely naked”.

His lawyers’ statement of claim describes how a soldier poured water on to Rahmatullah’s face after placing a cloth over his mouth and nose causing “a sensation of drowning”.

He was shackled and hooded, and lapsed in and out of consciousness as he was beaten and thrown against a wall. He was suspended upside down and “repeatedly dunked into a tank of water”, says the court document.

At one point, he was taken to a room “where he was horrified to see six or seven naked detainees piled on top of each other”, according to the court statement. He was thrown on top of the detainees and kept in the room for more than two days.

Despite an agreement signed by Britain and the US that specifically referred to the rights of prisoners of war and detained civilians enshrined in the Geneva conventions and international humanitarian law, Rahmatullah was handed over to US forces who secretly took him to Afghanistan. His entire body, including his eyes and mouth, were “taped tightly with duct tape”, the court document says. He was locked in a solitary cell with rats and cockroaches. With other Bagram detainees, he was exposed to daylight in 2006, for the first time in two and half years.

After going on hunger strike, he was subjected to force-feeding on six separate occasions. Apart from limited communication with International Committee of the Red Cross (ICRC) representatives, he had no contact with the outside world, including his family, until 2010.

British officials, their “servants and agents”, were “recklessly indifferent to the illegality of their actions”, Rahmatullah’s lawyers have told the high court.

Kat Craig, legal director at the human rights group Reprieve, who has recently visited Rahmatullah, said he had been “through 10 years of frankly unimaginable horror”.

She added: “Now that he has finally been able to speak freely to his lawyers, there is no longer any doubt that the British government bears responsibility for his torture and illegal rendition to Bagram.”

Craig continued: “Yunus was robbed of 10 years in the prime of his life; a time when he wanted to find a career, choose a partner and build a family.

“The government must now come clean about the full extent of British involvement in this disgraceful episode in our history – only then will Yunus be able to move on and try to rebuild his life.”

Reprieve legal directors says there is ‘no doubt’ of British responsibility for torture and rendition of Yunus Rahmatullah: here.